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Frozen storage of meat and meat products

25, Frozen storage of meat and meat products

TheoretICaIIy･ there are c一ear di什erences between the envlrOnmental conditions required for

cooiing･ Which iS a heat removailtempe｢ature reduction process, and those required for storage where

the aim IS tO maintain a set product lemperature･ However, in many air based systems cooiing and

storage take p一ace in the same chamber and even where Mo separate向ciiities are used, m many

cases not ai一 the required heat is removed in the coo一ing phase･ This faliure to remove the required

heat can be due to a number of causes,

inSu飾cient time aiiowed ,

inSu飾cient refrigeration capacity to cater for high initia一 product 一oad ,

overloading,

varlab掴ty in Size of products,

inCOrreCt enVirOnmentai conditions

ExtensiVe daねare availabie on the optimum Storage COnd-tiOnS and a他nable五〇zen storage

iiVeS for many products (iiR, 2000, iiR, 1986, ASHRAE, 1974).

25,1 STORAGE LiFE TERMS

There are a wide range of rather confusing de師tions used to de¶ne storage 一ife. The EC

directive (Commission of the European Community, 1984) states simp一y that frozen storage mustapreserve the intrinsic Characteristics" of the fo｡d･ A一though this IS Probably every food technoiogist's

aim, many d肺erent criteria can be used to measure these characteristics. The iiR recommendations

(1986) deme什ozen storage鵬as being "the physica一 and bi°ChemlCai reactions WhiCh由ke p一ace in

什°zenゐod products 一eading to a gradua一, cumulatiVe and irreversib一e reduction in product qua一ity

such mat e備er a period of time the product is no 一onger Suitab一e for consumption Or the intended

process競　ThiS definition tends to indicate that a什ozen product may deteriorate unti同is in a very

poor condition before storage 一ife ends, and so rather contradicts the EC de傭nitIOn.

liR (1986) recommendations a一so inc一ude the ten of practiCal storage眠(PSL). PSL iS

deflned as `the perlOd of frozen storage aHer freezlng during which the product retains its

characteriStlC properties and remalnS Suitab一e for consumption or the intended process'･ Bagh-

Sorensen (1984) describes PSL as `the time the product can be stored and stiII be acceptab一e to the

consumer'･ Both of these de軸tions of PSL depend on the use of sensory pane一s, 一eading tO the

d珊cuity of de惰ning aCCeptablilty and seiectlng a pane一 that represents consumers.

Another term referred to 'S `h'gh qua一ity life'(HQL)I This concept Yas deve一oped in the`Aibany'experImentS Sta白ed ln 1948･ HQL iS "the time e一apsed between freezing °f an initiaiiy high

quality Product and the moment when, by sensory assessment, a statistICaIIy signlficant difference

(P<0･01)五〇m the initiai high qua一ity (Immediate一y aner freezing) can be es屯biIShed" (iiR, 1986). The

cont｢oi iS Stored at -40oC or co一der to m涌mise qua一ity changes･ A一though weii suited to research

wo｢k, some drawbacks have been noted

The actua一 definition Of storage 一ife and the way it is measured has therefore been wide一y 一en

to the assessment of lndIViduai authors･ in some cases sensory assessment has been coupied with

chemICai or instrumenta一 tests, which a一though probab一y more repeatable than human judgements,

are again used at the auth°｢'s discretion Food techno一ogists have no standard way of est而ating

she一f iife･ Researchers have used many d附erent methods of assessing Samp一es, OHen with iittie

thought of the initial quaiity･ P'e-freezing treatment o':IZe Ofthelr SamPies･ This deGc･ency has 一ed to

poor conc一usions and recommendations that can be mISIeading tO users Of the data.

25,2　FROZEN STORAGE

ThIS Chapter iS a brief summary of a糾i review by James a Evans (1997). The factors that

州uence the storage 一ife of什ozen meat may act ln any One Of three stages: Prior tO freez-ng, during

the actua一 freezing process and post打eezlng in the storage period itse一f.

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⑥ 2008, UniVerSlty Of Bristo一 (FRPERC)

Frozen storage of meat and meat products

25･2･1 exidative rancidity

The importance of fat oxidatIOn in frozen meat IS IIlustrated by a short quotation from a paper

pubi'shed by Lea (1931) "it iS Onen the deterioration °f the融which I'mits the storage嶋一打Om the

POlnt Ofview at 一east ofpaiatab航y一〇川e meat"･ This View has been reiterated many times, and as

freezing techno一ogy has improved it IS true tO Say that向t oxidation remains the obstac一e to very 一ong

term storage of frozen meat･ Early studies on fat oxidation and freezing were reviewed by Lea (1938)

and Watts (1954).

25.2. 1, 1　　　The meclIanism of oxidaficn

The reaction of oxygen with fatty acids produces peroxides it iS the breakdown products of

the peroxides that`produce the characteristic OPjectIOnabie odour and f一avour of rancid meat The

deve一opment of oxidative rancidity in meat is a鴨cted by two groups of factors, one group consisting

of the bullt-I-haracterisdcs of the meat and the other group consistlng Of those factors Involved lnthe treatment of the meat･ The brmer are main一y under the contro一 of the farmer or are imate

characteristics Of the 一iving animaI･ whereas the ianer can be contr°iied by the abanoir, the meat

Packer or the co一d store operator･ A一though the面st group camot be changed by the meat processor

lt iS necessary tO consider their e仔ects so that procedures may be mod桶ed to ilmit them. Before

discussing eimer group it iS necessary tO 一ook at the process of fat oxldation in the hope that

kn°Wiedge of the process wiii indicate the ways in Which it may be controiied.

The reaction of oxygen with向t is an aut｡cataiytiC prOCeSS･ Once the reaction Stahs, the

products of the reaction Stimu一ate it to go faster･ The inlliai reaction is that between a molecule of

oxygen and a fa請y acid to brm a peroxide･ This iS a Si｡w reaction but 一ike any other chemica一

reacdon its rate IS increased by raislng the temperature The rate is also lnqUenCed by the type of

fatty acid･ Saturated fatty acids react slowly･ but unsaturated tatty aclds react more rapldly, and the

more doub一e bonds that a tatty acid contalnS･ the more reactlVe it iS･ The presence °f peroxides in fat

does not change the ¶avour, It IS the breakdown products of the peroxides which produce the rancid

odour and navour･ The breakdown of peroxide IS acce一erated by heat, 一ight, organic iron cata一ysts

and traces ｡f me由i ions, eSpeCiaIIy copper and iron･ it iS a一so the breakdown products of the

peroxides that cause the oxygen to react more rapid一y with the fatty acids, thus producing the

a utocataiytic e惰ect.

The type of fatty acid present in the meat is therefore of maior Importance in determlning its

oxldatiVe Stabiiity･ Beef and Mutton taIIow･ both very hard fats･ which contain few unsaturated fatty

aclds are much more stab一e than 一ard, a softer fat･ which contains a large quantity of unsaturated fany

ac'ds･ The effect of fauy acid compositl0n Can however be much more subtle･ Lea (1936) Observed

that feeding an ounce Of cod 一iver oi一 per day to pigs -nCreaSed the susceptibi一ity Of the fat to oxidation

by a tactor of Gve. a一though the change in the iodine va一ue of the fat was negiigibIe･ This resu一t may

be compared with the studies ｡f Dahi (1957) where an increase in the iinoleiC acid content of plg勧

什om 7% to 15･6%, which Increased the iodine number by ten面ts, on一y reduced the oxidative

stabillty tO Pne quarter･ The reason for the difference is that the quantity of polyunsaturated fatty

acids打om the cod iiVer Oi一 that was stored in the p一g自twas smaii

contained four, ¶ve and six doub一e bonds, the面tiation of oxidation

where the high iodine …mber was produced by an mcrease in a

bonds The reiatIVe SuSCeptibiy of oleiC, ilnOieic and iinoienIC acids,

bonds respectiVely, to oxidation iS 1 :12:100 (Kuhn a Meyer, 1929).

25.2. 1. 2　　　　Natural antioxidanfs

in view Of the ease with which向t oxidatIOn takes p一ace one

in the IivIng anima一, and if not, why not? The answer lS that lt does

does it OCCur in meat lmmedIateiy a償er siaughter･ The reason iS the presence in the ammai tissues of

antI-OXIdants that prevent the peroxide breakdown products from catalysing the oxidatIOn The major

ant主oxidan白n meat iS a-tOCOpheroi or vitamin E･ Deficiency of vitamin 管 in many anima一s 一eads to

the oxidation of the adipose I,ssue, wh,ch turns yeIiow (Dam, 1957). Such materia怖om pigs wou一d of

course not pass Inspection, but even meat having a 一owered tocopheroI content wou一d be 一ess stab一e

in什ozen storage･ The situation IS Weli documented in the case of the turkey, which has 一ow ieveis of

a-tocophero上　The向ection of a-tocopheroI into turkeys decreased the thiobarbiturIC acid va一ue, a

measure of oxidatiOn, Ofthe frozen carcass and mproved the鳴vour (Webb ef aI., 1972).

2

◎ 2008, UniVerSity of Bristo一 (FRPERC)

However, since these向慣y acids

was much easter than in the恰t

fa請y acid with on一y two d°uble

wlth one. two and three double

might enquire whether it occurs

but on一y to a smaii extent. Nor

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Frozen storage of meat and meat products

Fatty acld composltion and the antI-OXidant status ot the tISSue are the main factors affectlng

oxldatIOn, WHICH are fIXed in the anlmal before slaughter･ The fatty acid composltion of the dlet

readi一y changes the語録y acid composition Of plg向t, but has i剛e e鵬ct ln ruminants. The anti一

〇Xidant leveis of the tissues are not great一y a惰ected by changes in the quantity ln the diet, since iittie

of the added tocopherol血ds its way to the向t･ However, pro一onged 一ow ieveis of tocopheroi in the

diet Can reduce the quantity in the anima一 Feeding high levels of p°iyunsaturated fa地y acids can a一so

reduce the body's stores because of the extra.quantity needed to prevent oxidation･ The t｡C｡pheroi

content of cerea一s may be reduced if the grain iS Sta一e and the iipids have started to oxidiSe and

destroy iL Not ai一 the fat depots on the carcass are equaiiy susceptlbIe to oxidation. Subcutaneous

向t in most Species iS much softer, that iS more unSaturated, than the interna一 fat.

25･ 2･ 1, 3　　　Phosphol¢ids

Aithough the bu一k of the向t in a Carcass IS面the viSIbleねt depots, aII ceiis m the animai's

body contain phosphoIIPids as part of their structure･ Furthermore, the phospholipids contam large

quantities Of po一yunsaturated fatty ac-ds that are not readi一y in仙enced by the nature of the dietary

fa的acids･ The greater susceptibi母of phosphoiiPIds to oxidation compared with the neutra一 iipids of

gromd pork was obseNed by Younathan a W負ns (1960). Phosphoilpids have been used as anti一

〇xidants under certain COnditions, but the mechamsm by which they function iS not understood and it

iS not known if they exhibit any anti一〇xidant activity In什esh meat.

25.2.2　Pre･freezing treatment

Some pre-freezlng factors, I.e. SPeCIeS difEerences. animal to animal variation or differences

between cuts of meat, are inherent ln the animai･ There are a一so other向ctors inc一uding feeding and

transport that may have an affect on frozen storage.

Species is the main pre巾eezing向ctor that is common一y be一ieved to in¶uence the frozen

storage iife･ Tabie 1 provides data from three sources on the storage 一ife of meat什om di的rent

species and the average and range from ai一 the pubiiCati°nS 一ocated.

Tabie 1 〟 Frozen storage 一ife (months)向r d肝erent species (Source: James a Evens, 1997)

Source　　　　　　1　　　　　2　　　　　3　　　　　Average at Range at

Temperature(｡C )　　　-20oC　　　　-1 8｡ C　　　　-1 8oC　　　　　　-1 8c c　　　　　　　　_1 8o C

Species

Bee(　　　　　　　12　　　　　12　　　　　18　　　　　　　10 2　　　　　　　　2.8-194

Pork　　　　　　　　　6　　　　　　　8　　　　　　12　　　　　　　17 4　　　　　　　　2 8-23 3

Lamb lO　　　　　12　　　　　　24　　　　　　　　7.8　　　　　　　　2 8-24 3

ChiCken　　　　　　　12　　　　　10　　　　　18　　　　　　　13 6　　　　　　　　6 0-23 3

There iS Up tO a tWOわid di鵬rence between species in recommended storage times but more

impohantiy the relatiVe ranking, in terms of which can be stored for the 一ongest time, varies beMeen

the sources When all the avallable data found in the IIterature are considered the picture becomes

even more confusmg･ Average values for the storage lives of the different species at -18cc (Table 1 )

have a d嗣erent ranking to that generaiiy accepted and the range of storage iiVeS iS Very iarge･

Few pub一ications COmpare the meat of more than two species under direct一y comparab一e

conditions Under simi一ar a9-ng and packaging regimes beef was bun° to store for 69 weeks, pork

for 53 weeks and iambね｢44 weeks at -18oC At -18oC pork remained paiatabieめr 一onger than 一amb

but at higher temperatures the 一amb was more stabie･ it seems軸r to conc一ude that most work points

towards a di僧erence, but not necessarily a consistent d肺erence, in frozen storage 一ife between

species

To 一ook at anima一 t° anima一 variation two tria一s were carried out in New Zeaiand where iamb

was stored at -5cc･ In the flrSt trial the Iamb was judged rancid after 20 Weeks and ln a duplicate trial

the 一amb was found to store for 40 weeks･ The on一y variation that cou一d be determ活ed was that

different animals were used in the two trlals･ There appear to be large variations between animals

which cause changes m the storage 一ife of meat but why these d一倍erences exist is not completely

understood.

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⑥ 2008, UniVerSity of Bristo一 (FRPERC)

Frozen storage of meat and meat products

Feeding Influences frozen storage life･ Pork from plgS that had been fed materlals contalnlng

o的l or househo一d refuse had hair the practica一 storage 一ife than that什Om pigs that had been fed

conventional dletS (Bailey et all, 1973)I Rat10nS With large amounts of hlghly unsaturated fatty aclds

tend to produce more unstab一e meat and向t･ The feeding of筒sh olis or high一y unsaturated vegetab一e

oils to poultry IS known to produce fishy flavours in the meat but there IS SOme debate as to whether

this diet direCtiy a的cts frozen storage times The iinoieic acid content of meat probab一y p一ays a maJOr

ro一e ln StOrage･ There has been a genera一 trend ln the UK In recent years for pigs tO be 一eaner and

therefore to have greater p｢opohiOnS Of ilnOIeiC acid in their tissues･ There is a poss嗣ty that pork

may store 一ess weil than might be expected from resu一ts dating from 10 or 20 years ago

Repons of va｢Iations in the storage 一ife of d肺erent cuts of meat are scarce and primariiy show

tha川ght meat stored br a 一onger time than dark meat･ This is thought to be due to either higher

quantities Of haem p一gments ln the dark musc一e, or t° higher quantities of phospholiplds which are

major Contributors to oxldiSed f一avour in cooked meat

increased stress or exhaustion can produce PSE (pa一e so備and exudalive) or DFD (dark冊m

and dry) meat, which is not re∞mmended for storage main一y due to its una的actiVe nature and

appearance.

Meat lS generaiiy no出ozen unt掴gor is comp一ete and a degree of conditiOmg has taken

p一ace, othe…ISe tOughe-g and increased drip can occur･ In red meat, there is i聞e evidence of any

re一ationship between ch柵ng rates and frozen storage iiね･ However, there iS evidence that Increasing

the time in chiiied storage beわre freezing reduces frozen storage 一ife. Carcasses which have been

eiectricaIIy stimu一ated have pro一onged storage 一ives and this C°uld be ambuted to the shoher inteNai

betweer"laughter and freezing ln poultry･ chilllng method does have an effect of storage llfe･ Air

c間ed broi一ers had slg南cant fiav｡ur changes a鵬｢ 3 months at -12｡c and -20℃, whereas

immersion chiiied birds on一y exhibited changes at -12oC a償er 6 months and were stab一e al _20｡C.

Water chiiiing Of broi一ers produced a more自vourable taste in the 一eg and breast meat than air Chliilng

Processlng Of meat prior tO什eezlng generaiiy resu一ts ln a 一engthened storage time･ Heating

pr10'tO freezing Can resu一t in a 50% 一onger PSL (Practica一 Storage LIfe) Gor sausages. However, the

heamg process cou一d be critica一 since musc一es cooked to higher temperatures are most susceptib一e

to oxidatIVe Changes during storage･ Heat treatments such as frying tend to produce shoh storage

livesi probably because ｡f the hlgh fat content of the product･ Breaded products are onen fried and

a一though b'eading a一one may have a protective effect on a product言he addition of oli may have a

cou nteractive effect

A process such as m活cing has beenわund to a托ct storage of comminuted products言his IS

probab一y due to the induced heating and the increased suHace area mat resu他. Addition Of向t to

rpinee can 一ower storage life un一ess a high grade wrapping materia一, wh-ch has the abi一ity to exc一ude

alr･ lS used to wrap the product･ Smoklng IS generally advantageous due to the antIOXIdant propertleS

of the smoke･ Smoked broilers and ham store well for over a year wlthout sehous quality change.

AdditiVeS･ Such as spices, Seasoning, anti°xidants and protein COnCentrateS Can innuence

storage ilfe The use of vegetab一e extracts such as onion lulCe, yellow onion pee一, hot water extracts

ot aubergine (egg plant)I Potatoes and sweet potatoes have been shown to help control rPncidny.n

beef and turkey meat However, an addition of sai一 may a一so reduce the storage腫due to Increased

rancldity･ MechanICaiiy recovered meat iS used in a噂nge of meat products, but can cause storage

prob一ems due to its high fat content and increased rancidity.

25･2･3　The Freezing Process

There are few data to suggest that in genera一 the method o的eezing or the rate ｡f打eezing

has any substantia白いfiuence on a food's subsequent storage 一ife There IS Some disagreement in the

一iterature as to whetherねst (cryogeniC) or si｡W (b一ast) freezing iS advantageous. SIIghtiy superior

chemica一 and sensory attributes have been found ln Sood cryogenlCaily frozen in a few trials, but other

tria一s did not show any appreciab一e advantage, especlaliy during Sho齢 term storage･

The mem°d of什eezing CiearIy a的cts the uitrastructure of the meat. S一ow freezmg (1-2

mm/hou" for example) tends to produce la'ge ice crystals extraceliuiariy･ whi一st quick freezipg (e g･ 50

mmlhour) gives Smaiier crysta一s ln and outside celis. Obviously, a temperature gradient wlii occur ln

large pleCeS Of meat and result ln a nO-n-unitorm ice morphology･ Fast freezlng tends to produce a

llghter coloured product as the small ice crystals scatter the IIght more than larger crystals and this

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⑥ 2008, University of Bristo一 (FRPERC)

各iS

8i

Frozen storage of meat and meat products

enhances the suHace appearance of pou一try skin However, there are no data to suggest that the

uitrastructure in¶uences storage 一ife.

25.2.4　During Frozen Storage

Three factors during storage, the storage temperature, the degree of網uctua高on in the

storage temperature and the type of wrappinglpackaging in which the meat iS Stored, are common一y

belieVed to have the main inf一uence on frozen storage 一ife.

25. 2.4. 1　　　Sto愉ge femperature

To quote from the ilR Red book " storage life of near一y ai一 frozen foods IS dependent on the

temperature of storage･･･''and in the book a由bie iS provided of practica一 storage 一ives of di沌rent

bods at three storage temperatures, extract in Tab一e 2. However,向w papers have been 一ocated

where data are presented什om experiments On the PSL of meat at d碓erent storage temperatures

Many of those that have been 一ocated are on products that do not meet the 一ower temperature 一onger

storage ru一e (nomai stabi一ity).

Table 2･ Practica一 storage 一ife (months) at different storage temperatures (source liR, 1986)

Product　　　　　　　　　　　-12oC　　　　　-18oC　　　　　-24oC

Beef carcasses

Beef steakslcuts

Ground beef

Veai carcass

Veal steakslcuts

La mb carcasses

Jamb steaks

Pork carcasses

Pork steakslcuts

SiiCed bacon (vac )

Chicken. who一e

Chicken pahslcuts

Tu爪ey, who一e

Ducks, Geese, who一e

LiVer

8　　　　　　　15　　　　　　　24

8　　　　　　　18　　　　　　　24

6　　　　　　　10　　　　　　　15

6　　　　　　　12　　　　　　　15

6　　　　　　　12　　　　　　　15

1 8　　　　　　　24　　　　　　　>24

12　　　　　　　18　　　　　　　24

6　　　　　　　10　　　　　　15

6　　　　　　　10　　　　　　　15

12　　　　　　　12　　　　　　　12

9　　　　　　　18　　　　　　　>24

9　　　　　　　18　　　　　　　>24

8　　　　　　　15　　　　　　　>24

6　　　　　　　12　　　　　　　18

4　　　　　　　12　　　　　　　18

Experimentai data from many d楯erent pubiicatiOnS have been pio請ed against the

temperature of storageねr beef (Figure 1), pork (Figure 2) and Iamb (Figure 3) There iS a C一ear e傭ect

of temperature on storage i艇, with 一ower temperatures resuitlng in extended storage, but

considerab一e scatter beMeen resu一ts at any one temperature.

it has been shown that rancidity in bacon is inc｢eased by higher sail content and that the

rates of chemica一 reactions are acce一erated as the temperature iS 一owered when packed in Permeab一e

wrap･ Cured pork products are known to have an abnorma一 temperature profiie between -5oC and -

60cc and store 一ess weii between -30oC and -40cc.

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⑥ 2008, University of BrIStOl (FRPERC)

Frozen storage of meat and meat products

0　　　0　　　0　　　0　　　0　　　00　　　0　　　0　　　0　　　0　　　0?-0(‥o64.?-

(sFep)JaeqJoaJlla6eJo)S

-40　　　　-30　　　　-20　　　　-1 0

Temperature (oC)

Figure 1 I Experimenta一 data on storage 一ife of beef at d楯erent temperatures (source: James a

Evans, 1997)

0　　　0　　　0　　　0　　　0　　　00　　　0　　　0　　　0　　　0　　　0?-0864?-

(S^ep)NJ°duooJII e6eJ°〕S

-40　　　　-30　　　　-20　　　　-1 0

Temperature (oC)

Figure 2･ Experimenta一 data on storage 一ife of pork at d紆erent temperatures (source: James a

Evans, 1997)

0　　　0　　　0　　　0　　　0　　　00　　　0　　　0　　　0　　　0　　　0?-Ono64?-

(S(ep)qEe二〇aJlla6eJO〕S

｡　　●　　場.

-40　　　　-30　　　　-20　　　　-10

Temperature (oC)

Figure 3･ Experimenta一 da由on storage 一ife of Iamb at d肺erent temperatures (source: James a

_　Evans,1997)

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Frozen storage of meat and meat products

r Improved aroma scores have been found to be moderately related to lower freezing

temperatures･ but not re一ated to navour･ Aroma scores for minced beef improved during 6-12 month

storage a1 -12 2oC･ -17･8oC or -23･3℃, a一though a s一ight increase in rancidity a一so occurred

Work in New Zeaiand (Winger, 1984) has found that consumer pane一s are o鵬n not very

sensitive to qua一ity Changes and cou一d not teii the d田erence between samp一es of iamb stored at -5

and 35cc･ A tralned taste panel could differentlate between the two temperatures and scored the

sampies stored a主50C as rancid.

国書

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25. 2.4. 2　　　7empera fure 〝ucfuatねn

GeneraIIy, f一uctuating temperatures in Storage are considered to be detrimenta一 to the

product However: it has been repoHed that repeated什eeze-thaw cyc一es do not cause any essentiai

change in the musc一e uit｢astructure (Carroi ef all, 1981 ) and that severa一 freeze-thaw cyc一es during a

product's 一ife cause on一y smaii qua一ity damage (Wれh, 1979) or p°ssibiy no damage at ai一 in fact, a

s一ight but sign摘cant improvement in samp一es that had been frozen and un frozen severa一 times was

found by one taste panel (Jut, 1982).

Minor temperature f一uctuations in a stored product are generaiiy considered ummpOnant,

especiaiiy if they are be一ow -18oC and are on一y °f the magnitude of 1 to 2oC Weii packed products

and those that are tight一y packed in paiietised canons are a一so 一ess likely to show qua一ity i°ss.

However poor一y packed samp一es are severe一y a的cted by the temperature swings. There iS

disagreement On how much e的ct 一arger temperature帥ctuati°nS have on a product. Some authors

consider temperature血ctuatiOnS have the same e胎ct on qua一ity of the product as storage at an

average cons向nt temperature (Dawson, 1969), others c°nsider血ctuatIOnS may have an additive

e簡ect (Van Arsdei, 1969; Bech-Jacobsen & Bagh-Sqrensen 1984). There is evidence that exposure

to temperatures above -18oC rather than temperature mctuations may be the major factor infiuencing

qua一ity deterioration (Gohne｢ et aI., 1948).

25･2･イ･ 3　　　Packaging

Packaglng has a 一arge direct effect o.n storage life, especiaiiy ln tatty foods and in extreme

cases indirectiy due to substantlaiiy …creasing the freezing time･ A number of examp一es have

occurred where 一arge paliet 一oads of warm boxed meat have been什ozen in Storage rO°mS･ in these

cases･打eezing times Can be so great that bacteria一 and enzymiC activity resu一ts in a reduction of

storage Iife･ ln most cases言t is the materia一 and type of packaging that軸uences frozen storage 一ife

Wrapping in a tightiy柵ng pack having a 一ow water and oxygen permeabi一ity (Such as a vacuum

pack) can more than doub一e the storage鵬Of a product Waterproof packing a一so he一ps to prevent

freezer bum and的ht packing he一ps to prevent an ice bui一d up ln the pack When a produc白s

Dreaded, packaging appears to have littie e惰ect and in a tria一 where Dreaded pork chops and breaded

ground pork were packed in poor and very good packs an e什ect of packing cou一d not be found

Rancidity occurs in unwrapped meat because its Su鳴∞ dries, aliowing OXygen tO reach

subcutaneous tat･ Wthout wrapplng. freezer bum may occur causlng extreme tOughemng and thedevelopment of ranc'dlty ln the affected area･ Packaging can be effective ･n sonie cases ･n reducing

discolouratIOn by lessenlng oxygen PenetratIOn Into the meat･ Lighting, especlally ultra-vl01et, can

also Increase fat oxldatIOn (VoIZ et all, 1949; Lent2, 1971) Exposure to the levels of llght found ln

many ｢etaii什ozen food disp一ay areas ′can cause appreciab一e co一our change within 1 t° 3 days.

Deve一opment of o伴僧avour can be acce一erated and may be noticeab一e within 1 to 2 months on disp一ay

Products kep白n dark or opaque packages may therefore be expected to retain co一our 一onger than

those exposed to the 一ight.

25,3　TYPES OF STORAGE ROoM

25･3･1 Bu一k storage rooms

Most unwrapped meat and poultry and all types of wrapped foods are stored in large air

circu一ated rooms･ To minimlSe Weight 一oss and appearance changes associated with desiccation air

movement around the unwrapped product Shou一d be the m面mum reqいred to mainぬin a consねnt

temperature･ With wrapped products 一ow air Velocities are a一so desirab一e to m面mise energy

consumptiOn･ However･ many storage rooms are designed and constructed with岨ie regard to air

7

⑥ 2008, University of Bristo一 (FRPERC)

Frozen storage of meat and meat products

distrlbutIOn and locaIISed velocitleS ever Products HorIZOntal throw refrlgeratIOn COils are open

mounted ln the free space above the racks or raIIs of product and no attempt lS made to distribute the

air around the products

Using a矧se cei一ing Or Other form of ducmg to distribute the air throughout the storage room

can substantiaiiy reduce variations in ve一ocity and temperature Using air socks it iS c一aimed that an

even air distribution can be ma-ntained with iocaliSed ve一ocities not exceeding 0.2 ms-1.

25･3･2　Controiied atmosphere storage rooms

Controlied atmosphere storage rooms were deve一oped for speciaiISed血it stores, especiaiIy

those for apples･ ･ Interest is growing in the appiicati｡n Of this technique to other c°mmoditleS

inCi血ng meat･ in addition to the norma一 temperature contro一 p一ant these stores a一so inc一ude specia一

gas-tight sea一s to maintain an atmosphere which is normaIIy 一ower in OXygen and higher in …trogen

and carbon dioxide than air･ AddltiOnai p一ant iS required to contro一 the CO2 COnCentration, generate

nitrogen and consume oxygen.

There is growing interest in the use of controiied atmosphere retai一 packs to extend the chiIIed

storage and display胎°f red mea一s, poui叫and meat products･ Since the packs tend to be 一arge

and insu一ate the products e簡cient Ore-COOiIng before packagmg is especialiy imPO鳴nt if product

qua一ity iS tO be maintained

25.3.3 Jacketed co一d stores

Cooiing the waiis, 仰oor and ceiilng ｡f a store produces very good temperature contro一 in the

enc一osed space w-th the m面mum of air mOVement･ It is espec馴y sultabie for CA storage and for

unwrapped produce that are very sensitive to alr movement Or temperature fluctuatIOnS The

refrigerated Jacket can be provided by embedding pipe COiis in the structure or utiiISing a doub一e skin

construct10n through whICh refrlgerated air is clrCulated.

Aithough the re伽gerated jacket iS e紬ent in absorbing any heat input什om the surroundings

the 一ack of air circu一ation w柵n the enc一osed space means that heat remova川om the product is very

ilmited･ Care must therefore be taken lo (a) a嶋in the desired storage temperature throughout the

product beわre storing, (b) minimlSe any heat 一oads produced during 一oading and unioading, and (C)

provide the supp一ementary refrigeration required for any products which respire.

25,4　SUMMARY PolNTS

1)　Aithough a great dea一 has been wmen on the frozen storage 一ife of d肺erent mea一s the

underlylrlg data are backed up by a relatively small number of controlled sclentlfic

experiments･ Much of the scjen師c da向date back to the time when meat was either st°red

unwrapped or in wrapping materia一s that are no 一onger used･ it is not surprISing When we

conslder the changes ln PaCkaglng and handling methods over the last century that there is a

considerabie sca慣er in data on storage 一ives for simi一ar products.

2)　in recent years energy conseNatiOn requirements have caused an Increased interest in the

posslbi吋of using more e緬cient Storage temperatures than have been used to date.

Researchers such as Ju川ave questioned the wisdom of storage be一ow -200C and have

asked whether there is any rea一 economic advamage in very 一ow temperature preseNation.

There iS a growing reaiisatiOn that storage liVeS Of severa一 foods can be 一ess dependent on

temPerature than previous一y thought Since research has shown that meat and pou一try o償en

produce non ilnear time-temperature cuNeS there iS probab一y an optimum storage

temperatu｢e br a pahiCuiar product.

3) improved packing and p'eseNation of products can a一so increase storage 一ife and may ailow

higher storage temperatures to be used･ One suggestion lS that with storage a1 -18･C, low

stability mea一s such as mechanically recovered meat shou一d be stored br 8 months or 一ess,

medium Stabi吋meats such as pork and processed mea一s shou一d be stored for between 8

and 15 months, and high s屯biiity meats･ which lnCiude ai一 meat and pou-try except pork,

couid be stored for more than 15 months.

8

@ 2008, UnlVerSlty Of Bristol (FRPERC)